lawn fertilizer & flower bed
Jefferson County Colorado flowers: annuals and herbaceous perennials
How would you describe "not doing well"? Are they dying out? Is the above ground growth thin and scraggly? Do the plants look more yellow than the other plants in the garden? Do they turn brown during the growing season? Have they attained their expected height?
I suspect that if xeric plants are growing at the low end of a slope, water from the lawn runoff is likely an issue. Excess water applied to xeric plants can cause rampant growth, yellowing/dropping leaves and root rot. The plants could exhibit any or all of these symptoms. Excess fertilizer could cause rampant growth, but not root rot or yellowing, dropping leaves. I really don't suspect fertilizer is the cause.
Other factors that could cause poor plant growth of xeric plants could be compacted soil and excessive mulch.
You could check the soil around the plants after an irrigation to see if water if going where you want it to go - or if too much is being applied in some areas.
You can also send me a photo of the area is this occurs again and we'll go from there.